1. Field of the Invention
The present invention relates to a recording medium having tracks for recording information. The present invention also relates to a signal recording method and apparatus for recording a signal on the signal recording medium. The present invention also relates to a signal recording/reproducing apparatus for recording a signal on the signal recording medium and reproducing the signal from the signal recording medium.
2. Description of the Related Art
As a recording medium used for recording and reproduction, an optical disk is known. Such a recording medium has a recording surface (or recording layer). The recording surface has spiral tracks. A signal is recorded in a track groove (groove) or between a track groove and another track groove (land). Examples of a recording medium for recording a signal in a groove are a CD-R, CD-RW, DVD-R, and DVD-RW. An example of a recording medium for recording a signal on both a groove and a land is a DVD-RAM. In actually recording a signal, a mark corresponding to the signal is formed on a track by a laser beam.
Tracks on a recording medium are wobbled. When wobbling on a track is detected, a wobbling signal is obtained. A reference clock for a signal write can be obtained using the wobbling signal as a reference phase. More specifically, a write reference clock can be generated using an oscillation output equivalent to a signal obtained by frequency-multiplying the wobbling signal) from a PLL (phase-locked loop circuit) phase-locked to the wobbling signal.
With this method, a predetermined recording density can be obtained independently of the linear speed of the recording beam. In addition, even before the rotational speed of the disk reaches the fundamental speed, a signal write can be started. These effects are remarkable and employed as a recording scheme for various kinds of recording media described above. A CD-R or CD-RW uses a wobbling signal as a carrier wave and modulates and records a physical position signal. When the wobbling signal is detected, the physical address can be detected and used for search for information recording/reproduction.
The recording capacity of an optical disk has increased from a CD system using a laser wavelength of 780 nm to a DVD system using a waveform of 650 nm. A next-generation optical disk using a violet laser beam with a wavelength of 405 nm has been recently researched and developed. In this research and development, measures have been sought which make a recording mark small using a smaller laser beam diameter and consequently greatly improve the recording density and recording capacity. As another technique, a disk having stacked recording layers has also been researched and developed. A recording layer with a multilayered structure has already been employed by a DVD-ROM as a read-only disk. A rewritable RAM disk can also improve the recording capacity by employing this technique.
Currently available DVD optical disks are a DVD-RAM, DVD-R, and DVD-RW. A DVD optical disk can record a 4.7-GB digital signal on one surface of a 12-cm diameter disk. A DVD-ROM as a read-only disk has already implemented a two-layered structure on one surface and has a capacity of 9 GB on one surface. A recording medium with a two-layered structure has already been realized at the laboratory level and is expected to be put into mass production soon. In such a two-layered disk, to identify a recording layer subjected to recording and reproduction, layer identification information must be embedded in advance. Conventionally, a method of inserting layer identification information to control information data has been employed.
For example, in a DVD, ID information of each sector contains data “layer number” as “sector information”. The recording layer subjected to recording and reproduction can be identified by reading the “layer number”. However, in recognizing the contents of “sector information”, a read block is read in a sector synchronous state, error-correcting processing is executed, and then, the contents are recognized. If an inter-layer jump occurs or recording operation is to be quickly stopped, the necessary layer identification information cannot be detected at early time.
In a DVD-ROM system, an inter-layer jump can abruptly occur do to a defect or vibration during reproducing operation. When such inter-layer jump occurs, read data is demodulated as reliable data by error correction and the like, and after that, it is determined on the basis of an ID or the like contained in the read data whether the data is desired information. If it is determined that the data is not desired information, the information is discarded, and re-read operation is executed. This only requires an extra read time and poses no other problem.
However, if an inter-layer jump occurs during recording operation in the recording/reproducing system, recorded correct data is destroyed, resulting in serious problem. If an inter-layer jump occurs due to an operation error, and large block data, e.g., large data that cannot be error-corrected is destroyed, the block data cannot be restored. That is, when a recording error occurs to cause movement to another track due to an operation error, it is preferable to detect the recording error state and stop the recording operation at early stage while the error remains within the error-correcting ability of the system.